Avoid nullpointererror.

enrich-citygml-with-greenarea/src/main/java/de/hft/stuttgart/citygml/green/osm/GreenEnricher.java

@@ -18,7 +18,6 @@ import java.util.Set;
 import java.util.UUID;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-
 import org.citygml4j.core.model.CityGMLVersion;
 import org.citygml4j.core.model.building.Building;
 import org.citygml4j.core.model.core.AbstractCityObject;
@@ -63,7 +62,6 @@ import org.xmlobjects.gml.model.geometry.aggregates.MultiSurfaceProperty;
 import org.xmlobjects.gml.model.geometry.primitives.AbstractRingProperty;
 import org.xmlobjects.gml.model.geometry.primitives.LinearRing;
 import org.xmlobjects.gml.model.geometry.primitives.SurfaceProperty;
-
 import de.hft.stuttgart.citygml.green.osm.jaxb.OSM;
 import de.hft.stuttgart.citygml.green.osm.jaxb.OsmMember;
 import de.hft.stuttgart.citygml.green.osm.jaxb.OsmNode;
@@ -204,7 +202,6 @@ public class GreenEnricher
 	}
 
 
-
 	public static void createTransformers(CityModel cityModel) {
 		String epsgCode = extractEpsgCode(cityModel);
 		sourceCRS = CRS_FACTORY.createFromName(epsgCode);
@@ -218,7 +215,7 @@ public class GreenEnricher
 			WaterBody wb = new WaterBody();
 			org.xmlobjects.gml.model.geometry.primitives.Polygon poly = convertToCityGmlPoly(waterArea.getArea());
 			if (poly == null) {
-//				System.out.println("Skipping WaterBody " + waterArea.getArea());
+				//				System.out.println("Skipping WaterBody " + waterArea.getArea());
 				continue;
 			}
 			MultiSurface ms = new MultiSurface();
@@ -233,7 +230,7 @@ public class GreenEnricher
 		for (GreenArea ga : greenAreas) {
 			org.xmlobjects.gml.model.geometry.primitives.Polygon poly = convertToCityGmlPoly(ga.getArea());
 			if (poly == null) {
-//				System.out.println("Skipping " + ga.getArea());
+				//				System.out.println("Skipping " + ga.getArea());
 				continue;
 			}
 			PlantCover cover = new PlantCover();
@@ -349,7 +346,7 @@ public class GreenEnricher
 				GreenArea area2 = greenAreas.get(j);
 				if (area1.getArea().intersects(area2.getArea())) {
 					Geometry difference = area1.getArea().difference(area2.getArea());
-//					System.out.println(difference);
+					//					System.out.println(difference);
 					if (difference instanceof MultiPolygon) {
 						MultiPolygon multi = (MultiPolygon) difference;
 						Polygon poly1 = (Polygon) multi.getGeometryN(0);
@@ -478,7 +475,7 @@ public class GreenEnricher
 				if (member.getRole().isBlank()) {
 					// assume outer ring
 					// check if this ring is closed
-					if (coordinates.get(0).equals2D(coordinates.get(coordinates.size() - 1))) {
+					if (!coordinates.isEmpty() && coordinates.get(0).equals2D(coordinates.get(coordinates.size() - 1))) {
 						// ring is closed, create a polygon out of it
 						Polygon polygon = GEOM_FACTORY.createPolygon(coordinates.toArray(new Coordinate[coordinates.size()]));
 						coordinates.clear();
@@ -840,7 +837,7 @@ public class GreenEnricher
 			Road road = new Road();
 			org.xmlobjects.gml.model.geometry.primitives.Polygon poly = convertToCityGmlPoly(roadArea.getArea());
 			if (poly == null) {
-//				System.out.println("Skipping RoadArea: " + roadArea.getArea());
+				//				System.out.println("Skipping RoadArea: " + roadArea.getArea());
 				continue;
 			}
 			MultiSurface ms = new MultiSurface();
@@ -857,7 +854,7 @@ public class GreenEnricher
 			LandUse landUse = new LandUse();
 			org.xmlobjects.gml.model.geometry.primitives.Polygon poly = convertToCityGmlPoly(landUseArea.getArea());
 			if (poly == null) {
-//				System.out.println("Skipping RoadArea: " + landUseArea.getArea());
+				//				System.out.println("Skipping RoadArea: " + landUseArea.getArea());
 				continue;
 			}
 			MultiSurface ms = new MultiSurface();